The present invention relates to an expansible anchor and a method of making the same.
More particularly, it relates to an expansible anchor of metal having a bore and an expansible sleeve.
Expansible anchors and methods of their manufacture are known in the art. One of such anchors is disclosed for example in U.S. Pat. No. 2,685,221. The expansible anchor of metal disclosed in this reference is provided with a bolt which has several connected expander cones which form a thread. An expansible sleeve comprising two shells and provided with an internal thread is arranged on the expander cones. When the bolt is drawn into the expansible sleeve by a nut bearing against the article to be fastened, the expansible sleeve is pressed radially outwardly by the expander cones. Since the cones engage with the expansible sleeve over their entire length, the expansion of the expansible sleeve is substantially uniform over its entire length as well.
The expansible sleeve of the known expansible anchor includes two half shells provided with screw threads. When a bolt is drawn into the expansible sleeve, the half shells are pressed radially outwardly only in the expansion direction. Since the expansion direction is displaced by 90.degree. to the slot plane, a line contact of the two half shells with the expansible sleeve, despite high draw-in force, allows only low anchoring forces. An increase in the draw-in force also occurs as a result of the thread in the half shells of the expansible sleeve matched to the threads forming the expander cones. When the bolt is drawn in, the cone regions of smaller diameter of the expansible sleeve are displaced on the cone regions of larger diameter of the bolt. Therefore a greater pressure is exerted on the longitudinal edges of the half shells and, because of the rigidity of the half shells, increases the draw-in force without reinforcing the expansion effect and therefore the holding force of the expansible anchor. Moreover, in the known expansible anchor the two shells have to be held on the bolt of the expansible sleeve by wire rings.